The present invention relates to an apparatus and method of measuring the movement of groundwater and, more particularly, to a remotely operating semi-continuous flow rate logging seepage meter for measuring the movement of groundwater seepage into surface water bodies on a semicontinuous basis and for logging the measured information.
The environmental concern for inland and coastal water bodies has led to a considerable amount of research for defining material input into these waters. Based on such research, the movement of groundwater and its associated solutes from upland regions has been linked to the degradation of receiving surface water bodies. Mechanisms responsible for advective transport of solutes within nearshore sediments include elevated upland hydraulic head (i.e., groundwater discharge), convective flows caused by thermal and salinity density differences, sedimentation, spatial variations in sea state (i.e., subtidal pumping), benthic boundary currents, and bioadvection. In addition to influencing water quality management efforts, such transport mechanisms are of biological and geological importance.
Macroscopic seepage rates of water across the sediment-water interface typically range from 0.0 to 5.0 L.cndot.M.sup.-2 .cndot.hr.sup.-1. Hydraulic head differences between overlying surface waters and interstitial water is on the order of millimeters for most nearshore environments. Given such low and varied flow rates and hydraulic head differences, current flow meter technology is inadequate and the measurement of such phenomena remains a technical problem.
Current efforts to measure the direct influx of water have conventionally been through a manually operated seepage measuring devices, such as that disclosed by D. R. Lee, in "A Device for Measuring Seepage Flux in Lakes and Estuaries," Limnology and Oceanography, 22: 140-147, 1977. A typical seepage meter generally includes an open-bottom cylinder covered by a vented lid that allows a water collection bladder to be attached. The seepage meter is placed into the sediment, and water entering the meter is collected into the collection bladder. After a certain amount of time and if the collection bladder is full, the full collection bladder is retrieved and replaced with a new bladder. This is typically performed by a diver. The amount of groundwater discharge is determined by the volume of water displaced per cross-sectional area of seepage meter per unit time.
However, such manually operated seepage meters are disadvantageous in that they require extensive manual intervention and work effort.
In addition, conventional apparatus and methods require divers to monitor and replace collection bags, and record the number of discharges over a given time period. This leads to only being able to obtain a small number of data samples, which in turn renders incomplete and sometimes inaccurate results.